XSCOM regions
=============

The top-level xscom nodes specify the mapping range from the 64-bit address
space into the PCB address space.

There's one mapping range per chip xscom, therefore one node per mapping range.

/
/xscom@<chip-base-address-0>/
/xscom@<chip-base-address-1>/
…
/xscom@<chip-base-address-n>/

- where <chip-base-address-n> is the xscom base address with the gcid-specific
  bits (for chip n) OR-ed in.

Each xscom node has the following properties:

 * #address-cells = 1
 * #size-cells = 1
 * reg = <base-address[#parent-address-cells] size[#parent-size-cells]>
 * ibm,chip-id = gcid
 * compatible = "ibm,xscom", "ibm,power8-scom" / "ibm,power7-xscom" 


Chiplet endpoints
=================

One sub-node per endpoint. Endpoints are defined by their (port,
endpoint-address) data on the PCB, and are named according to their endpoint
types:

/xscom@<chip-base-address>/
/xscom@<chip-base-address>/chiptod@<endpoint-addr>
/xscom@<chip-base-address>/lpc@<endpoint-addr>

- where the <endpoint-addr> is a single address (as distinct from the current
  (gcid,base) format), consisting of the SCOM port and SCOM endpoint bits in
  their 31-bit address format.

Each endpoint node has the following properties:

 * reg = <endpoint-address[#parent-address-cells] size[#parent-size-cells]>
 * compatible - depends on endpoint type, eg "ibm,power8-chiptod" 

The endpoint address specifies the address on the PCB. So, to calculate the
MMIO address for a PCB register:

	mmio_addr  = <xscom-base-addr> | (pcb_addr[1:27] << 4)
				       | (pcb_addr[28:31] << 3)

Where:

  - xscom-base-addr is the address from the first two cells of the parent
    node's reg property
  - pcb_addr is the first cell of the endpoint's reg property 
